Update default kerl to 4.0.0

[jjcarstens]

There seem to be some nice improvements since 2.6.0 that it may be worth having 4.0.0 as the default when not otherwise specified

[Stratus3D]

Testing locally it appears some things have changed for kerl and the asdf-erlang code no longer provides correct output. For example, with this new code when I run asdf list-all erlang I get:

17.5.6.10
18.3.4.11
19.3.6.13
20.3.8.26
21.3.8.24
22.3.4.26
23.3.4.19
24.3.4.15
*
25.3.2.8
*
26.2.1
*

which is incomplete and incorrectly formatted. I'm going to merge this PR and then fix the issues in another PR.

[Stratus3D]

Thanks for the PR @jjcarstens !